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Glossary of Lithography Terms - L


Latent Image The reproduction of the aerial image in resist as a spatial variation of chemical species (for example, the variation of photoactive compound concentration).

Example: The latent image was visible to the naked eye due to the change in the resist optical properties with exposure.


LER see Line Edge Roughness


LES see Line-End Shortening


Levenson PSM see Alternating PSM


Lifting, Resist The separation of the resist pattern from the substrate, either partially or completely, due to a loss of adhesion.

Example: Resist lifting could not be avoided without the use of an adhesion promoter.


Lift-Off Process A lithographic process by which the pattern transfer takes place by coating a material over a patterned resist layer, then dissolving the resist to “lift off” the material that is on top of the resist.

Example: The lift-off process allowed the patterning of the metal without the use of an etch step.


Line Edge Roughness (LER) The deviation of a feature edge (as viewed top-down) from a smooth, ideal shape. That is, the edge deviations of a feature that occur on a dimensional scale smaller than the resolution limit of the imaging tool that was used to print the feature.

Example: One simple measure of line edge roughness is the RMS deviation of an edge from a best-fit straight line.


Line-End Shortening (LES) The reduction of the length of a line (where a line is defined here as any rectangular feature whose length is significantly greater than its width) as measured only at one end. Thus, the line-end shortening is characterized as the difference between the actual position of the end of a line and the intended (designed) position.

Example: The amount of line-end shortening for the feature increased sharply when out of focus.


Linear Resolution The smallest feature that can be printed (using some agreed-upon criterion for resolution) while simultaneously allowing acceptable printing of all larger features.

Example: While the use of OPC does not improve the ultimate resolution of a lithography process, its main benefit is in improving the linear resolution.


Linearity The variation of printed linewidth as a function of designed (or mask) linewidth. In general, linearity is measured with a fixed duty cycle (equal lines and spaces, for example).

Example: The use of OPC resulted in a marked improvement in linearity for both dense and isolated lines.


Linewidth see Critical Dimension


Lithographer 1. A practitioner of lithography. 2. A harmless drudge.

Example: The overworked and underappreciated lithographer paused for a moment and daydreamed, “Will Moore’s Law ever end?”


Lithography A method of producing three-dimensional relief patterns on a substrate (from the Greek lithos, meaning stone, and graphia, meaning to write).

Example: Although lithography is a centuries-old patterning technique, the small features used in integrated circuits make semiconductor lithography very challenging.


LSI Large-Scale Integration, an integrated circuit made of hundreds to thousands of transistors.

Example: As integrated circuits entered the LSI era, contact and proximity printing gave way to projection lithography.